Magnetorheological fluid devices

ABSTRACT

This invention relates to sealless designs of magnetorheological fluid dampers. With these sealless designs a piston rod extends above and below a piston head within a cylindrical housing and has frustoconical elastomer elements attached to and between the rod and housing to allow translation of the piston head and rod. The piston head has a coil contained radially therein that produces magnetic flux in and around the piston. The advantages of utilizing an MR fluid according to the invention include magnetic fields which are easily produced by low voltage electromagnetic coils, damping effects which are velocity independent, and higher yield strength obtained by the MR fluid capable of generating greater damping forces.

This application is a sister application of Ser. No. 07/900,571 filedcontemporaneously herewith.

FIELD OF THE INVENTION

Incompressible fluids have been used in shock absorbers and otherdampers, as well as in elastomeric mounts, for decades. The use ofcontrollable fluids, electrorheological (ER) and magnetorheological (MR)fluids in dampers, was first proposed in the early 1950's by Winslow inU.S. Pat. No. 2,661,596. The use of a controllable fluid in damperaffords some intriguing possibilities relative to providing widelyvarying damping for varying conditions encountered by the damper.Nonetheless, the use of controllable fluids was generally restricted tothe area of clutches, with a few exceptions, until the mid-1980's.

BACKGROUND AND SUMMARY OF THE INVENTION

Interest in the use of controllable fluids revived in the 1980's asactivity in the area of controllable dampers increased. Most of theresurgent activity has occurred relative to ER dampers and associatedfluids. While interest and development of ER fluid devices continuesperformance of such systems have been disappointing from threestandpoints:

1) the damping forces that can be generated by an ER fluid device arelimited due to the relatively low yield strengths of the availablefluids;

2) ER fluids are susceptible to contamination which significantlydegrades performance; and,

3) the strong electric fields required by ER fluids necessitatecomplicated and expensive high-voltage power supplies and complexcontrol systems.

Faced with these performance restrictions and searching for atechnological breakthrough to overcome them, Applicants turned to MRfluids with renewed interest and sought to optimize systems employingthem. MR fluids inherently have higher yield strengths and are,therefore, capable of generating greater damping forces. Further,contamination does not pose the performance degradation threat for MRfluids that it does for ER fluids. Still further, MR fluids areactivated by magnetic fields which are easily produced by simple,low-voltage electromagnetic coils.

It is therefore among the objects of the present invention to provide anMR damper with improved performance characteristics. Enhancementsinclude:

defining dimensional/operational relationships which provide improvedperformance;

devising piston designs in which the flow path for the magnetic flux isentirely contained within the piston itself;

providing an improved twin-tube cylinder design capable of use (withsome modification) with either the self-contained or spool piston;

significantly reducing or eliminating MR fluid losses from the damper;

providing an improved fluid valve for controlling the flow of the MRfluid to produce the desired damping forces.

These and other objects of the invention are accomplished by anapparatus for variably damping motion using an MR fluid. The apparatusincludes a housing for containing a volume of MR fluid; a piston adaptedfor movement within the housing, the piston being formed of ferrousmetal, having a number, N, of the windings of conductive wireincorporated therein to define a coil that produces magnetic flux in andaround the piston; and having a configuration in which ##EQU1## whereA_(core) is a minimum lateral cross-sectional area of the piston withinthe coil, A_(path) is a minimum lateral cross-sectional area ofmagnetically permeable material defining a return path for the magneticflux, A_(pole) is the surface area of the piston's magnetic pole,B_(opt) is an optimum magnetic flux density for the MR fluid, andB_(knee) is a magnetic flux density at which the ferrous metal begins tosaturate.

The housing may be provided with a sleeve of ferrous material toincrease the cross-sectional area of the return flow path for themagnetic flux, A_(path), for configurations in which the return path forthe magnetic flux is through the housing. Alternatively, the housing maybe a twin-tube design; the magnet may be formed on a spool-shaped pistonor wound as a toroid thereon; the magnet could be positioned within thetwin-tube housing rather than on the piston; loss of MR fluid can beprevented by topping the damper with a less dense fluid, using a scraperand seal combination, or using a sealless design. The piston may beformed from conventional ferrous materials (in either solid or laminateform) or from powdered metals. These features may be embodied in a mountas well as in a damper.

Other features, advantages and characteristics of the present inventionwill become apparent after a reading of the following detaileddescription.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view in partial section of a first embodiment of the MRdamper of the present invention;

FIG. 2 is an enlarged side view in partial section of the pistonassembly depicted in FIG. 1;

FIG. 3 is schematic side view in partial section depicting thedimensional relationships of the first embodiment, the internal detailsbeing omitted for simplicity and clarity;

FIG. 4(a) is a graphic plot of flux density (B) vs magnetic fieldstrength (H) for a particular MR fluid;

FIG. 4(b) is a plot of B_(intrinsic) (J) vs field strength H for thesame MR fluid;

FIG. 4(c) is a plot of J² vs H for the same MR fluid;

FIG. 4(d) is a plot of flux density (B) vs field strength (H) for asteel used in making the piston and housing of the present invention;

FIG. 4(e) is a plot of flux density (B) vs field strength (H) for apowdered metal used in making the piston and housing of the presentinvention;

FIG. 5(a) is a peak force (F) vs peak velocity (V) plot for differentlevels of current for a first damper configuration, with extensionforces being shown as having negative values;

FIG. 5(b) is a peak force vs peak velocity plot for different levels ofcurrent for a second configuration which does not meet the preferredcriteria for ^(A) path/^(A) pole with extension forces being shown ashaving negative values;

FIG. 5(c) is a peak force vs peak velocity plot for different levels ofcurrent for a third configuration which does not meet the preferredcriteria for ^(A) core/^(A) pole with extension forces being shown ashaving negative values;

FIG. 6(a) is a peak force (F) vs current (A) plot for the firstconfiguration operated at a stroke rate of 0.2 Hz and an amplitude of±1.0 in. (peak velocity is 1.3 in./sec) with extension forces beingshown as having negative values;

FIG. 6(b) is a peak force vs current plot for the second configurationoperated at a stroke rate of 0.2 Hz and an amplitude of ±1.0 in. (peakvelocity is 1.3 in./sec) with extension forces being shown as havingnegative values;

FIG. 6(c) is a peak force vs current plot for the third configurationoperated at a stroke rate of 0.23 Hz and an amplitude of ±1.0 in. (peakvelocity of 1.5 in./sec) with extension forces being shown as havingnegative values;

FIG. 7 is a top view of a piston having a plurality of toroidally woundmagnet sections, with the rod sectioned;

FIG. 8 is an isometric view partially in section of the piston of FIG.7;

FIG. 9(a)-9(d) are cross-sectional side views of first through fourthpiston embodiments with incorporated internal valve structure;

FIG. 10(a) is a cross-sectional side view of a first twin-tube housingconfiguration;

FIG. 10(b) is a cross-sectional side view of a second twin-tube housingconfiguration;

FIG. 10(c) is a cross-sectional side view of a third twin-tube housingconfiguration employing two magnetic valves;

FIG. 11(a) is a schematic cross-sectional side view of a first seallessdesign;

FIG. 11(b) is a schematic cross-sectional side view of a second seallessdesign;

FIG. 11(c) is a schematic cross-sectional side view of a third seallessdesign;

FIG 12(a) is a schematic cross-sectional side view of a first mountconfiguration employing an MR fluid; and,

FIG. 12(b) is a schematic cross-sectional side view of a second mountconfiguration employing an MR fluid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the damper of the present invention is depicted inFIG. 1 generally at 16. Damper 16 is made up of two principalcomponents: housing 20 and piston 30. Housing 20 contains a volume ofmagnetorheological (MR) fluid 18. One fluid which has shown itself to beparticularly well-suited for this application consists of carbonyl ironparticles suspended in silicone oil. This MR fluid has a relativemagnetic permeability between 3 and 15 at a magnetic flux density of0.002 telsa (20 gauss). An MR damper has two principal modes ofoperation: sliding plate and flow (or valve) modes. Components of bothmodes will be present in every MR damper, with the force component ofthe flow mode dominating.

Housing 20 is a generally cylindrical tube with a first closed end 22with an attachment eye 24 associated therewith. A cylindrical sleeve 25may be affixed to the inner cylinder by any conventional means (e.g.,press fit, welding, adhesive) to increase the cross-sectional surfacearea of housing 20, as will be discussed in greater detail hereafter. Asecond, or open, end of the cylinder is closed by end member 26. A firstseal 27 extends about the outer periphery of member 26 to prevent fluidleakage between housing 20 and member 26. A second annular seal 28 ishoused in a groove in the inner periphery of member 26 and seals againstshaft 32. A scraper 29 can be used to wipe the MR fluid off the surfaceof shaft 32 so as to minimize loss of MR fluid past seal 28. As anadditional means of preventing fluid loss, the upper regions of housing20 can be filled with a second fluid which is immiscible with MR fluidor which can be separated from the MR fluid volume 18 by a floatingbaffle or rolling diaphragm (not shown).

Housing 20 is provided with a floating piston 21 to separate the MRfluid volume 18 from pressurized accumulator 23. While a floating piston21 is shown, other types of accumulators can be used and, in fact, aflexible rolling diaphragm of the type shown in U.S. Pat. No. 4,811,819is actually preferred. Accumulator 23 is necessary to accommodate fluiddisplaced by piston rod 32 as well as to allow for thermal expansion ofthe fluid.

The first embodiment of piston assembly 30 is shown in greater detail inFIG. 2. Piston head 34 is spool shaped having an upper outwardlyextending flange 36 and a lower outwardly extending flange 38. Coil 40is wound upon spool-shaped piston head 34 between upper flange 36 andlower flange 38. Piston head 34 is made of a magnetically permeablematerial, such as low carbon steel, for example. Guide rails 42 areattached around the outside of piston head 34 at particular intervals.As shown in FIGS. 1 and 2, four guide rails 42 are shown spaceduniformly about the periphery of piston head 34. Piston head 34 isformed with a smaller maximum diameter (in this case, D_(pole), in FIG.3) than the inner diameter, D_(I) of housing 20. The external surfacesof guides 42 are contoured (radiused) to engage the inner diameter D_(I)of housing 20. Guides 42 are made of non-magnetic material (e.g.,bronze, brass, nylon, brass, nylon, or Teflon® polymer) and maintainpiston centered within gap `g`. In this embodiment, gap g (inconjunction with coil 40) functions as a valve to control the flow of MRfluid 18 past piston 34.

Electrical connection is made to coil 40 through piston rod 32 by leadwires 45 and 47. A first wire 45 is connected to a first end of anelectrically conductive rod 48 which extends through piston rod 32 toPhono-jack connector 46. The center connection of Phono-jack 46 isconnected to a first end 39 of coil 40. The second end 41 of thewindings of coil 40 is attached to a "ground" connection on the outsideof Phono-jack 46. The electrical return path, then, includes piston rod32 and the ground lead 47. The upper end of piston rod 32 has threads 44formed thereon to permit attachment of damper 16, as depicted in FIG. 1.An external power supply, which provides a current in the range of 0-4amps at a voltage of 12-24 volts, depending upon application, isconnected to the leads 45 and 47. An epoxy bushing 49 keeps rod 48isolated from return path through piston rod 32. The cavity surroundingconductive rod 48 may also be filled with epoxy. The outer surface ofcoil 40 may be coated with epoxy paint as a protective measure.

The damper 16 of this first embodiment functions as a Coulomb or Binghamtype damper, i.e., this configuration approximates an ideal damper inwhich the force generated is independent of piston velocity and largeforces can be generated with low or zero velocity. This independenceimproves controllability of the damper making the force a function ofthe magnetic field strength, which is a function of current flow in thecircuit.

FIG. 3 schematically depicts the dimensional relationships of the damper16. The minimum diameter of the spool-shaped piston head 34 is thediameter of the core, D_(core), and the diameter of the coil 40 isD_(coil) while the length of the coil 40 is L_(coil). As already noted,the gap or valve has a thickness g and the length of the pole is thewidth of flanges 36 and 38, which is also the length L_(g) of gap g. Theinside diamter of housing 20 is D_(I), the outside diameter is D_(O),the maximum diameter of the piston is D_(pole) (making ##EQU2##

Efforts to optimize the performance of this embodiment of MR damper hasled to identifying several key relationships interrelating dimensions toits operational parameters. In basic terms, the flow of magnetic fluxwill be heavily dependent on several critical "bottlenecks" in the flowpath:

A_(core) --the minimum lateral cross-sectional area of piston head 34within the windings of coil 40, having a value of ##EQU3## A_(path) --aminimum lateral cross-sectional area of magnetically permeable materialdefining a return path for magnetic flux, having a value of ##EQU4##A_(pole) --a surface area of a magnetic pole of the piston, having avalue of πD_(pole) L_(g).

One design consideration is to minimize the amount of steel, i.e., tomake A_(core) and A_(path) as small as possible. However, it has beenfound that the ratio of the bottlenecks A_(core), and A_(path) toA_(pole) should be greater than a minimum threshold value defined by theratio of the magnetic field strengths in the MR fluid and dampermaterials, giving rise to a competing design consideration. That ratiois ##EQU5## where B_(opt) is an optimum magnetic flux density in the MRfluid and B_(knee) is the magnetic flux density at which the ferrousmetal begins to become saturated.

The value for B_(opt) can be better understood by turning to FIGS.4(a)-(c). FIG. 4(a) is the plot of the responsiveness of the MR fluidearlier described to magnetic field strength (magnetic flux density B vsmagnetic field strength H). The magnetic flux density B has twocomponent parts: B_(intrinsic), that is, solely attributable to thefluid, and a magnetic field component having a value of μ_(o) H, whereμ_(o) is a magnetic permeability constant, and H is the strength of themagnetic field which can be approximated by multiplying the number ofturns N in coil 40 times the current I through coil 40 divided by twicethe gap g. B_(intrinsic), or the magnetic polarization J, as it is alsoknown, is equal to the total flux density B less the componentattributable to the field strength. That is,

    B.sub.intrinsic =J=B-μ.sub.o H

FIG. 4(b) is a plot of J vs H for the same MR fluid represented in FIG.4(a). It is difficult to identify, with any precision, where the optimumoperational point is for this MR fluid by looking only at FIG. 4(b). Thecurve suggests that there is a non-linear increase in the value of B forH values between 100,000 and 318,000 A/m (1300 and 4000 oersteds). Amore definitive method of determining a value of B_(opt) is to plot thesquare of J vs H. This curve is shown in FIG. 4(c). B_(opt) isassociated with the field strength H at which the slope of the J² vs Hcurve ##EQU6## that is at the point of tangency to the curve for thecurve's secant tangent. For this MR fluid and, indeed, for many of thefluids which have been tested, B_(opt) occurs at a value of H=100,000A/m (1300 oersteds), and for this fluid has a value of 0.635 telsa (6350gauss) as seen in FIG. 4(a).

While this is a valid operational criteria, it is desirable to have asmuch energy in the fluid as possible and as little in the steel; thatis, operationally we would like the ratio of ##EQU7## to be as large aspossible where E_(f) is the energy in the fluid and E_(s) is the energyin the steel. E_(f) and E_(s) are given by the following expressions:

    E.sub.f =1/2B.sub.f H.sub.f V.sub.f

where V_(f) is the operational volume of fluid, and

    E.sub.s =1/2B.sub.s H.sub.f V.sub.s

where V_(s) is the operational volume of the steel.

Since, V_(f) ≈2A_(pole) g

and V_(s) ≈A_(core) L_(s), then ##EQU8## where L_(s) is the length ofthe entire flux path through the steel.

The damper 16 must be operated below B_(knee) for the steel as shown inFIG. 4(d), for conventional steels and FIG. 4(e) for powdered metals. Itis readily apparent that H_(s), and hence E_(s), go up quite rapidly forincrease in H above the value corresponding to B_(knee) with little orno increase in the flux density, B. From FIG. 4(d), B_(knee) has a valueof 1.4 tesla (14000 gauss). By way of example, then, for this MR fluidand this steel, the ratio of B_(opt) to B_(knee) has a value of 0.454.More generally, this ratio should be greater than 0.4. The dimensionalparametric ratios should be greater than or equal to this criticalvalue. The value for powdered metals will be larger since B_(knee)occurs at a smaller value.

The B_(opt) taken from FIG. 4(c) represents a minimum value. B_(opt) canhave higher values than B=0.635 tesla, so long as the flux density inthe steel is not greater than B_(knee) and as long as the ratio ##EQU9##remains equal to or less than the bottleneck ratios, ##EQU10## Byincreasing B_(opt) above 0.635 tesla (6350 gauss), up to a maximum ofabout 1.011 tesla (10,110 gauss) at H=279,000 A/m (3500 oersted) forthis configuration, more energy is input to the fluid while maintainingthese desired operational parameters. This increases the ratio ##EQU11##enhancing performance. What these relationships really tell the damperdesigner is that beyond a certain point, it is necessary to depart fromrule 1 (minimize A_(core) and A_(path)) in order to permit additionalenergy to be input into the fluid, rather than operating the damper inan inefficient operational zone (e.g., above B_(knee)).

In order to demonstrate the importance of these relationships, threedampers were constructed and tested. The dimensions of these dampers areshown in Table I.

                  TABLE I                                                         ______________________________________                                                Damper #1 Damper #2   Damper #3                                       ______________________________________                                        D.sub.core                                                                               34 mm       30 mm       30 mm                                      D.sub.pole                                                                               43 mm       42 mm       42 mm                                      D.sub.o    57.2 mm     57.2 mm     57.2 mm                                    D.sub.I    46 mm       46 mm       46 mm                                      L.sub.g    10 mm        8.8 mm     15 mm                                      N         199 turns of                                                                              125 turns of                                                                              125 turns of                                          23 gauge wire                                                                             22 gauge wire                                                                             22 gauge wire                               A.sub.core                                                                               908 mm.sup.2                                                                              707 mm.sup.2                                                                              707 mm.sup.2                               A.sub.pole                                                                              1350 mm.sup.2                                                                             1161 mm.sup.2                                                                             1978 mm.sup.2                               A.sub.path                                                                               908 mm.sup.2                                                                              908 mm.sup.2                                                                              908 mm.sup.2                                ##STR1## 0.673       0.608       0.357                                        ##STR2## 0.673       0.260       0.459                                       ______________________________________                                    

As was mentioned earlier, one desirable characteristic of an MR damperis for it to be velocity independent. FIGS. 5(a)-(c) establish that adamper made in accordance with these parameters achieve velocityindependence. The three dampers used to construct Table I were testedunder substantially similar conditions and the results are plotted inFIGS. 5(a)-(c), respectively. Damper 1 meets the criteria for bothratios of A_(core) and A_(path) to A_(pole), (i.e., both values areequal to or exceed 0.454), while Damper 2 is below specification forA_(path) and Damper 3 is below specification for A_(core). As the FIGS.5(a)-(c) indicate, the performance for Damper 1 is substantiallyvelocity independent, while those for Dampers 2 and 3 are not (as isindicated by the slope of the curves). Further, the optimizedconfiguration of Damper 1 is capable of achieving significantly highercompression (positive) and extension (negative) forces for the samelevels of current, as compared to those achievable by Dampers 2 and 3.

These results are confirmed by the plots shown in FIGS. 6(a)-(c) whereinforce is plotted vs current for these same three dampers forsubstantially similar stroke rates and stroke lengths. Specifically,FIG. 6(a) for Damper 1 and FIG. 6(b) for Damper 2 were taken at a strokerate of 0.20 Hz, an amplitude of ±1.0 inch and a peak velocity of 1.3in/sec. Data for FIG. 6(c) for Damper 3 were taken at a stroke rate of0.23 Hz, an amplitude of ±1.0 inch and a peak velocity of 1.3 in/sec.

FIGS. 7 and 8 depict a second embodiment of the piston 30 useful indamper 16. In this embodiment, coil 40 is toroidally wound about a coreelement 43, which may be of low carbon steel or powdered metal.Actually, the toroidal coil is formed by four segments 50 with theterminal wire from one segment initiating winding of the adjacentsegment 50. In between segments 50 are four valve slots 52 to permitfluid flow through piston 30. Twin seals 54 extend about the peripheryof piston 30 and engage the inner diameter of housing 20 (FIG. 2) tocreate a fluid seal. The MR fluid 18 is, therefore, forced to flowthrough slots 52 and control of the flow of current through coil 40 canclosely control the flow characteristics of the MR fluid.

Four additional alternative embodiments of the piston 16 are depicted inFIGS. 9(a)-(d). FIG. 9(a) depicts an embodiment in which coil 40 iswound on core element 43 and slipped into cup member 53. Cup member 53has a plurality of passageways 56 formed therein, has twin seals 54extending about the periphery, and is attached to core element 43 bymeans such as threaded fasteners, not shown.

The ram effects of the fluid will be undesirable for certainapplications and FIGS. 9(b)-(d) disclose various baffle plate designs tocope with this problem. FIG. 9(b) is the first such baffle plate design.Coil 40 is wound upon a thin, cylindrical non-magnetic sleeve 55 whichis then received in cup-shaped member 53. The internal portions ofcup-shaped member 53 including contained passageways 56 can easily bemachined prior to insertion of coil 40.

Baffle plate 58 is retained in position by non-magnetic supports 51which may be adhered to the surface of plate 58. Cup-shaped member 53 isformed with an extension 62 which is threaded onto piston rod 32. Endcap 64 fits within the lower end of coil 40 and may be retained there byconventional means (fasteners, welding or peripheral threads engaginginternal threads in cup-shaped member 53). A central hole 66 in end cap64 permits flow through the piston, baffle plate 58 serving to diminishram effects and extending the length of the fluid path in which the MRfluid is under the influence of the magnetic field. A hole 57 mayoptionally be provided in plate 58, depending upon the desired flowcharacteristics.

In this (FIG. 9(b)) embodiment, the return path for the magnetic flux isthrough the radially outer reaches of piston head 34, with D_(I) beingthe inner dimension of the flow path and D_(O) being the outer dimensionthereof. D_(B) is the diameter of the baffle plate 58, D_(P) is thediameter of the pole (the inside diameter of the coil) and D_(H) is thediameter of the hole 66. The diameter of baffle plate hole 57 is D_(N).The magnetic flux will pass through the most apparently "solid"magnetically conductive path, (i.e., with only minimal gaps and noobstructions).

The critical bottleneck dimensions are, then, expressed as follows:##EQU12##

Each different geometry has its own associated equations which defineits operational characteristics.

FIG. 9(c) depicts an embodiment in which piston head 34 contains asingle passageway 56 with a lateral, partially circular portion. FIG.9(c) depicts this lateral portion as extending through 180°, althoughthe passageway could obviously extend through a larger or a smallercircular arc.

FIG. 9(d) depicts an alternate baffle plate embodiment in which the coil40 is wound upon the end of piston rod 32. Care must be taken with thisembodiment to make the core portion 43 of piston rod 32 of sufficientdiameter to avoid saturation of the core.

Each of the embodiments discussed thus far, incorporate the magneticcoil 40 into piston head 34. In some applications it may be preferablefor the coil to be associated with housing 20, if housing 20 is morestationary, to minimize flexing of wires. The three embodiments shown inFIGS. 10(a)-(c) each employ a twin-tube housing 20 which allow the coil40 to be located stationarily relative to the housing. Housing 20 has afirst inner tube 17 and a second outer tube 19. Valve member 59comprises coil 40 which is wrapped around core element 43 and the end ofinner tube 17 is stabilized between core element 43 and cup-shaped endmember 53 by spacers (not shown) to define the gap g of valve member 59.Accumulator 23 is incorporated into piston head 34. As shown, a floatingpiston 21 can be used to create the accumulator 23 or, as mentioned withrespect to earlier embodiments, a rolling diaphragm of a type similar tothat taught in U.S. Pat. No. 4,811,919, which is hereby incorporated byreference, may be used. Any type of accumulator may be used.

As the piston 30 experiences a compressive stroke, the MR fluid is a)forced through gap g, which (in conjunction with coil 40) functions as avalve, b) into outer tube 19, c) through openings 68 back into the innertube 17. The flow characteristics of MR fluid 18 will be controlled byregulating the current flow in coil 40, as with previous embodiments.

FIG. 10(b) shows a similar twin tube housing 20 in which coil 40 istoroidally wound about core 43 in segments with intermittent slots as inthe FIG. 8 embodiment. The slots, in conjunction with the coil 40 willfunction as the valve for the MR fluid 18 in this embodiment.

FIG. 10(c) demonstrates a third embodiment of a damper 16 which has atwin tube housing 20. In this embodiment, two coils 40 are used, thelower coil 40 and gap g₁ form the valve for controlling flow of thecompressive stroke while upper coil 40 and gap g₂ form the valve forcontrolling flow on the extension stroke. Lower valve member 59 isdepicted as having a baffle plate 58, while upper valve member 59, whichmust permit passage of piston rod 32, is of a modified solenoidaldesign. Upper and lower check valves 35, which are preferably reedvalves that flap open and closed responsive to fluid pressure, providefluid bypass of upper and lower coils 40 for the compression andextension strokes, respectively.

An externally mounted accumulator 23 of the type shown in U.S. Pat. No.4,858,898 is used in this embodiment which comprises an elastomericbladder that may be filled with air or foam rubber. As with the otheraccumulators, accumulator 23 provides room for additional incompressibleMR fluid resulting from displacement by piston rod 32 or from thermalfluid expansion. In this embodiment, no electrical connections are madethrough piston rod 32 and piston head 34 has a more conventionalengagement with inner tube 17 (i.e., no fluid flow past or through).Recesses 37 form pockets which in conjunction with hydraulic end stops31 trap fluid and prevent piston head 34 from banging into either endcap 64. This double-valve design is particularly useful for dampersgenerating large forces. In such applications, the use of two valves 59provides more precise control and reduces the risk of cavitation of thefluid. Further, the forces generated in the compression and extensionstrokes can be individually tailored to fit the desired designparameters.

FIGS. 11(a)-11(c) depict three embodiments of sealless dampers 16. Oneproblem with the conventional damper design is preventing loss of the MRfluid which would result in diminished performance. Previously describedembodiments have proposed the use of a secondary fluid with acombination scraper and seal to cope with this problem. A secondaryproblem is the need for an accumulator with the conventional designs toprovide for fluid displaced by the piston rod. With the sealless designsof FIGS. 11(a)-(c), the piston rod 32 extends above and below pistonhead 34 and has elastomer elements 70 and 72 which may be offrustoconical design, bonded to its upper and lower extents,respectively. Elastomer elements 70, 72 are also bonded to housing 20trapping a fixed volume of fluid 18. An accumulator is unnecessary sincethere is no fluid displaced by piston rod 32 which cannot beaccommodated by the volume on the opposite side of piston head 34.Depending on the bulge stiffness of the elastomer, the elements 70 and72 can accommodate thermal expansion of the fluid. Electrical connectionis made to coil 40 through shaft 32, as in earlier embodiments. Also, aswith earlier embodiments, gap g, in conjunction with coil 40, functionsas a valve to control fluid movement and piston 34 subdivides housing 18into first and second fluid chambers 18a and 18b, respectively. Ears 74(FIG. 11(a)) provide means for attaching housing 20 to one of the twoelements to be isolated with piston rod 32 being attachable to theother.

The embodiment of FIG. 11(b) affords a means of providing greaterresistance to compressive forces than to extension forces bypressurizing (or charging) chamber 76.

FIG. 11(c) shows a third sealless embodiment designed to provideextended stroke. As shown in FIG. 11(c) damper 16 is shown at thecompletion of a compression stroke. Disc shaped elastomer 70 is bondedat its outer extremity to a ring 77 which sits atop the inner cylinderof housing 20 and its inner periphery is bonded to element 80, which ispreferably metallic. The upper inner periphery of element 80 slidesfreely relative to piston rod 32 by virtue of bearing 82. The lowerinner periphery of element 80 is bonded to the outside of disc-shapedelastomer 71 whose inner 32 but its use (being separable therefrom)facilitates manufacture.

A second element 80 has the outer periphery of disc-shaped elastomer 72bonded to its inner upper periphery. The inner periphery of disc 72 isbonded to piston rod extension 33. A fourth disc-shaped elastomerelement 73 is bonded to the outer lower periphery of second element 80and to ring 78 which is trapped between portions of housing 20 and,functionally, becomes a part thereof. This embodiment permits the throwlength of damper 16 to be extended and, obviously, additional throwlength could be added as necessary by stacking additional elements 80with associated disc-shaped elastomers 70-73.

A pair of mounts employing the features of the present invention aredepicted in FIGS. 12(a) and 12(b) generally at 86. The embodiment ofmount 86 in FIG. 12(a) has a baffle plate 58 which is held in place bysnap-in spacers 89, and a solenoid-type coil 40 wrapped within housing20. Spacers 89 are made of a non-magnetic, preferably plastic material.Baffle plate 58 diverts the flow of the MR fluid into more intimatecontact with coil 40 enhancing the flow control of the fluid byincreasing the capability of the coil to influence the characteristicsof the fluid. A first pair of bolts 91 provide means for attachment to afirst member (a frame, or the like) and bolt 93 provides means forattachment to a second member (an engine, for example). Elastomericelement 90 is bonded to both attachment collar 88 and housing 20 andcomprises the primary spring in the mount 86. Collar 88, elastomericelement 90 and upper surface of housing 92 for baffle plate 58 define afirst chamber 94 for containing MR fluid. The lower surface of housing92 and an elastomeric bladder 95 (which forms the bottom compliance ofmount 86) define a second chamber 96 for MR fluid. The orifices 98 inhousing 92 operate with coil 40 to define a valve for controlling theflow of the MR fluid, as in previous embodiments. The radial extent oforifices 98 is a design parameter which may be adjusted to influenceoperational characteristics of the mount 86.

The embodiment shown in FIG. 12(b) is similar to that shown in FIG.12(a) in all particulars with the exception that the coil 40 is of thetoroidal type with slots 52 serving as the fluid control valve as withthe twin tube design depicted in FIGS. 10(b). The slots 52 serve asmeans to increase exposure of the MR fluid to the coil 40, therebyenhancing flow control. No baffle plate is necessary with this design,so a solid divider plate 58a is substituted.

The mounts 86 of FIGS. 12(a) and 12(b) allow the stiffness of the mountto be controlled in response to operational characteristics of theengine (idle vs high rpm), or vehicle (cornering or straight runs) byuse of electronic sensors and control signals giving input to the energysupply of coil 40, in a conventional manner.

The present invention provides a number of embodiments of an MR fluiddamper with a variety of novel characteristics. A first embodimentoptimizes the dimensional and operational parameters of the damper toprovide a high level of controllability. A second embodiment provides analternate piston head with a toroidally wound magnet incorporatedtherein. Third through sixth embodiments provide piston heads with fluidflow therethrough (rather than therearound) and the magnetic flux pathcontained entirely within the piston head. A series of seventh throughninth embodiments provide alternate housing configurations in which theflow control magnet is associated with the housing, including oneembodiment in which an upper and a lower flow control valve is used.Tenth through twelfth damper embodiments teach sealless dampers whicheliminate loss of MR fluids and, finally, two MR fluid mount designsemploying the features of the present invention are described.

Various changes, alternatives and modifications will become apparent tothose of ordinary skill in the art following a reading of the foregoingdescription. For, example, while the piston motion being damped hasimplicitly been axial, it will be appreciated by those of ordinary skillin the art that dampers made in accordance with the specifics of thisinvention will be equally well adapted for damping rotary motion, orcombinations of linear and rotary motion, as well. Further, althoughelectromagnets have been described exclusively, it will be appreciatedthat permanent magnets may be utilized to provide some or all of themagnetic field. It is intended that all such changes, alternatives andmodifications as come within the scope of the appended claims beconsidered part of the the present invention.

We claim:
 1. Apparatus for damping motion between first and second relatively movable members, said apparatus comprising:a) a housing containing a volume of magnetorheological fluid; b) first means for attaching said housing to one of said movable members; c) a piston rod mounted for relative movement with respect to said housing; d) second means for attaching said piston rod to another one of said first and second movable members; e) a first block of elastomer interconnecting said housing and said piston rod, said block being fixedly attached to each of said housing and a first end of said piston rod, said block of elastomer forming at least a portion of a first fluid-containing chamber for said magnetorheological fluid; f) a second block of elastomer interconnecting said housing and said piston rod, said block being fixedly attached to each of said housing and a second end of said piston rod and, together with said first block, functioning as the sole means for permitting said piston rod to move relative to said housing, said second block of elastomer forming at least a portion of a second fluid-containing chamber for said magnetorheological fluid; g) a piston attached to an intermediate portion of said piston rod for movement therewith which divides said first fluid-containing chamber from a second fluid-containing chamber for said magnetorheological fluid, substantially all of the movement of said piston being accommodated by flow of fluid past said piston; h) valve means for permitting magnetorheological fluid to flow from and to said first fluid-containing chamber to and from said second fluid-containing chamber, said valve means includingi) aperture means for permitting said flow, ii) a magnetic coil associated with said aperture means for controlling said flow therethrough,whereby a desired level of damping of said relative movement is provided.
 2. Apparatus according to claim 1 wherein said aperture means comprises a gap formed between an outside perimeter of said piston head and an inside perimeter of said housing.
 3. Apparatus according to claim 2 wherein said magnetic coil is formed integrally upon said piston head.
 4. Apparatus according to claim 1 wherein said first and second blocks of elastomer is each comprised of a pair of disc-shaped elements, a first such disc-shaped element being attached about its outer periphery to said housing and about its inner periphery to an intermediate member adapted for movement with said intermediate member.
 5. Apparatus according to claim 4 wherein a second of said pair of disc-shaped elements has an outer periphery attached to an inner periphery of said intermediate member and an inner periphery attached to said piston rod.
 6. Apparatus according to claim 1 further comprising an auxiliary chamber associated with one of said first and second fluid-containing chambers, said auxiliary chamber being chargeable with a second compressible fluid to modify a response property of said piston head.
 7. Apparatus for variably damping motion using a magnetorheological fluid, said apparatus comprisinga) a housing containing a volume of magnetorheological fluid; b) a piston adapted for movement within said housing through said magnetorheological fluid, said piston connected to a piston rod for movement therewith; c) valve means includingi) a magnetic coil associated with said housing and said piston for modifying at least one flow characteristic of said magnetorheological fluid, and ii) passageway means through which said magnetorheological fluid flows; d) elastomer block means at each end of said piston rod, wherein each of said elastomeric block means is formed as twin disc-shaped elements, a first disc shaped element element being fully bonded about its outer periphery to said cylindrical housing and also having a cylindrical aperture which is fully bonded to an outer periphery of a first end of an interconnecting element and a second disc shaped element element which has a central aperture that is fully bonded about its inner periphery to a piston rod and about its outer periphery to a second end of said interconnecting element;whereby each end of said piston rod is fully sealed against loss of magnetorheological fluid. 